The report details how pipeline-monitoring staff in Enbridge’s Edmonton control room could not agree that a leak had occurred, while ignoring alarms that should have triggered a shutdown of the pipeline within 10 minutes of the leak occurring.

A school bus length section of the pipeline ruptured on July 25, 2010, pouring more than 20,000 barrels of diluted bitumen into a 60-kilometre stretch of the Kalamazoo River.

Two days ago, Enbridge reported it had completed the cleanup, but there are still reports of oil contamination along the river.

The National Transportation Safety Board is conducting an extensive investigation of how the leak occurred.

While the investigation is not finished, the NTSB has released several factual reports, including a 51-page document that details how Enbridge’s Edmonton pipeline-control room responded to the Kalamazoo leak.

The report says the company has a basic rule requiring any operator who discovers abnormal pressure or flow readings to shut down a pipeline within 10 minutes.

But the report says the controllers did not close valves on the pipeline until 17 hours after the leak, and only after they were alerted by a phone call from a worker on the ground in Michigan.

"The initial and subsequent alarms associated with the rupture were not recognized as a line break throughout two startup attempts and over multiple control-centre shifts," the report states.

Operators didn't know how to respond to alarms

The report details how operators were confused about the warning alarms or how they were to respond. They not only misdiagnosed the rupture, but twice tried to restart the pipeline while ignoring repeated alarms.

"Operator B2 said he has never seen this problem before and that it was interesting," the report states. "Operator B2 stated that the situation looked like a leak, and Operator B1 stated that they could pump as much as they wanted but never over-pressurize the pipeline.

"Operator B2 stated that eventually the oil has to go somewhere. Operator B2 said that it seemed as if there was something wrong about the situation. Operator B2 said to Operator B1, ‘Whatever, we’re going home and will be off for a few days.’ Operator B1 stated that they were not going to try this again [restart the pipeline)], not on their shift."

Enbridge declined an interview request from CBC News, saying it would not comment until the NTSB issued its final report. But in a release it said: "We have made several changes to the structure and leadership of functional departments such as pipeline control, leak detection and system integrity."

This most recent Enbridge leak, and the report, come at a time when a public-relations war is being waged over Enbridge’s proposed Gateway pipeline through northern British Columbia.

"I think both of those events have increased the opposition to the pipeline," Greenpeace campaigner Mike Hudema said Friday. "I think you’re going to see the opposition get bigger because Enbridge’s oil-spill track record is not a good one."